Single-driver based speaker on the horizon

Duke · « **on:** 29 Jul 2009, 07:06 pm »

My first commercial product was the "Cheetah", based on the Fostex FE206E "fullrange" driver but augmented by a built-in powered subwoofer and a supertweeter. The Cheetah actually used two FE206Es, in bipolar configuration. Unfortunately it wasn't a screaming commercial success, but I learned from it. The main problem was limited dynamic capability, probably due to the limited linear excursion capability of the FE206E. Since then I've kept my eyes open for a fullrange driver that can do significantly better in that department, and I think I've found one.

Initial tests have been encouraging, so I'll be building a prototype system in the near future, and will post updates here as the project develops.

bluemike · « **Reply #1 on:** 29 Jul 2009, 08:06 pm »

looking forward to hearing what else you have cooking Duke

I love reading your posts

opnly bafld · « **Reply #2 on:** 29 Jul 2009, 09:42 pm »

Quote from: bluemike on 29 Jul 2009, 08:06 pm

looking forward to hearing what else you have cooking Duke

I love reading your posts

Listening to his speakers isn't half bad either.

Lin

Duke · « **Reply #3 on:** 30 Jul 2009, 04:59 am »

Thanks for the encouragement!

It's unlikely that I'll overcome all the limitations that single-driver systems deal with, but I'm not ashamed to cheat if I think that will help (hence the name of my first commercial speakers).

The challenges and tradeoffs for a truly fullrange single-driver system are pretty daunting, so my first cheat is that I'm going to use a Swarm for the bass region.

rajacat · « **Reply #4 on:** 30 Jul 2009, 05:39 am »

As the owner of Omega Hemp Bipoles, I'm looking forward to your iteration of the single driver bipole form.

When I have guests over to hear my system the first remark is usually related to how clear the sound is and the second is surprise that the little 4-1/2" drivers can deliver room filling volume. In addition the excellent imaging confounds intuition since a bipole design should have a diffuse sound field because of the bouncing of the sound waves off the rear wall as well having the drivers are facing opposite directions. The sweet spot is wide and the imaging holds up well when you walk around the room. In fact it's somewhat holographic because when I'm between and in back of the speakers it seems like I'm on the same cloud as the band and part of the mix.

I have been running the Omegas with a sub but they do sound very good sans sub. I eagerly await trying them with a pair of Rhythmik open baffle subs.

I have tried running them with just the forward drivers but immediately switch back to the bipole configuration because it sounds soooo much better. aa

-Roy

Duke · « **Reply #5 on:** 30 Jul 2009, 11:25 pm »

Hi Rajacat,

Yup the Omega bipoles are excellent little speakers. I don't think there's any point in my trying to compete with Louis in the small fullrange bipole market, as I don't see room to improve on what he's doing there. So my system will take a different approach, with the mains only going down to 80 Hz or so, but then a subwoofer becomes a requirement rather than an option.

chadh · « **Reply #6 on:** 31 Jul 2009, 12:47 am »

Fantastic. Now that I have a swarm on the way (to pair with my Omega super 3xrs), it looks like I'll have another main speaker option to think about!

Keep us updated, Duke.

Chad

ttan98 · « **Reply #7 on:** 2 Aug 2009, 11:21 pm »

Duke,

Can you give us some idea what full range you will be using? Or is it still under wrap?

cheers.

Duke · « **Reply #8 on:** 4 Aug 2009, 07:40 pm »

Ttan, I can understand your curiosity but for now I'd like to keep the driver I'm using under wraps.

Duke · « **Reply #9 on:** 6 Aug 2009, 01:55 am »

Quote from: rajacat on 30 Jul 2009, 05:39 am

In addition the excellent imaging confounds intuition since a bipole design should have a diffuse sound field because of the bouncing of the sound waves off the rear wall as well having the drivers are facing opposite directions.... I have tried running them with just the forward drivers but immediately switch back to the bipole configuration because it sounds soooo much better.

The ear derives localization cues primarily from the first .68 milliseconds of sound, which corresponds to a path length of about 9 inches (approximately the length around your head from one ear to the other). Repetitions of the original signal (whether from a reflection or from a second driver) arriving after .68 milliseconds are largely ignored from a source-localization standpoint; this characteristic of human hearing is called the "precedence effect" or "Haas effect", after Helmut Haas who first described it in an AES paper many years ago.

Sound that arrives after that initial .68 millisecond window still contributes to perceived loudness and timbre. In general, it's desirable to have a significant time gap between the first-arrival sound and the onset of reflections because early reflections tend to be interpreted as coloration and late reflections tend to be interpreted as richness and spaciousness. Ten milliseconds or more, corresponding to a path length difference of at least 11 feet relative to the direct sound (or placing the speakers 5.5 feet out from the wall behind them), would be nice... but that's not always feasible. Based on personal experience with dipoles and bipoles, I would say that 3 feet out from the wall is probably a realistic minimum. Any closer that than, and unless you have some tricks up your sleeve (like heavily diffusing the backwave/rear driver energy) the net effect of the reflections is more likely to be detrimental than beneficial. That's why bipoles and dipoles don't sound good up against the wall.

As rajacat's experiment with monopolar configuration shows, when done right the net effect of the extra reverberant energy from rear-facing drivers is definitely beneficial even if it sure seems counter-intuitive to devote half your driver budget to drivers that don't even face you. Tonal balance was probably better as well, as the rear-facing driver pretty much offsets the baffle step.

Duke · « **Reply #10 on:** 8 Aug 2009, 10:28 pm »

What causes fullrange drivers to lose clarity and articulation on loud, complex passages? Is it doppler distortion? Nonlinearities in the midrange region from the voice coil going outside its linear limits on long bass strokes? Magnetic flux modulation?

I don't know for sure. Up until yesterday I thought linear excursion was the limiting factor.

I did some reading up on doppler distortion, and it looks like that's a greater problem in fullrange drivers than I'd previously appreciated. One researcher recommends keeping excursion below 1 mm peak-to-peak, and my system reaches 1 mm peak-to-peak at about 98 dB within its passband (and without a highpass filter). Taking into account that music energy is spread out over complex waveforms instead of focused into a sine wave, we can probably hope for 104 dB peaks without exceeding the 1 mm peak-to-peak threshold. This would still be a 6 dB improvement over the Cheetah.

If the limiting factor is the linear excursion, as I had come to believe before investigating doppler distortion, then my system should be good up to 113 dB on sine waves. That seems outrageously optimistic for a fullrange driver system, so I'm inclined to think that doppler distortion is more likely the limiting factor. But at least the surplus x-max my system has will keep cone motion linear and compression-free as we reach the theoretical doppler threshold.

If the limiting factor is flux modulation, well the motor on the drivers I'm using is better than most but probably not as good as the very best. I think it has a shorting ring; it's not spelled out but the inductance is amazingly low. Unfortunately I don't have a way of calculating flux modulation vs output level.

I'll come back to this topic when I've had a chance to do some investigation of my own.

opnly bafld · « **Reply #11 on:** 9 Aug 2009, 12:12 am »

Thanks for sharing your thoughts Duke.
I'm really looking forward to seeing and hopefully hearing this design.

Lin

DaveC113 · « **Reply #12 on:** 9 Aug 2009, 12:36 am »

The best sounding single driver speakers I've heard are capable of relatively large excursions, which are the Omega and Feastrex speakers... the Feastrex in particular can move like a subwoofer. Makes me wonder about the whole doppler distortion theory, and if it really makes as much difference as some seem to think.

Duke · « **Reply #13 on:** 11 Aug 2009, 08:51 am »

Opnly bafld, I appreciate your enthusiasm and encouragement very much. If they turn out well, I hope you get to hear them too.

Dave113, it would be great if you are right about large-excursion fullrange drivers sounding the best. Such has been my experience as well; the best-sounding fullrange driver I have heard is the 8" field-coil Supravox, which has an x-max of 4 mm. But I didn't hear it with the kind of music that makes fullrange drivers stumble, and don't know how much of what I heard was due to the ultra-high-quality motor.

Tonight I finished designing the equalization circuit for the driver I'll be using, and ordered enough parts to complete a stereo pair for ears-on evaluation. My ears help me to tell when there's still a problem that needs to be solved, but they are never good enough to tell me exactly where the problem is nor what needs to be done. For that, I go back to measurements. Hopefully my ears can later tell me if I got it right. So, I should probably say that I THINK I've finished designing the equalization circuit!

I realize that using equalization or contour circuits is not consistent with an ultra-purist approach, but I think that if done gently it can be a net benefit in many cases. I think it's a good idea to start out with a driver that doesn't need a lot of correction in the first place, which is why I chose the FE206E for the Cheetah, but I still used some equalization on it. Two different people at RMAF '05 told me the Cheetah was the best-sounding Fostex-based speaker they'd ever heard... unfortunately, neither of them were in the market for a Fostex-based speaker!

In a departure from the innovative enclosures often used with fullrange/wideband drivers, I'm using simple sealed boxes for the enclosures in this project, in hopes of protecting against over-excursion from loud deep bass without having to use a highpass filter. The Qtc is .85 and the calculated -6 dB point is about 85 Hz, [edit: 55 Hz in the production version, low-tuned vented box] so the latter is my projected ballpark crossover frequency to the Swarm.

Duke · « **Reply #14 on:** 24 Aug 2009, 04:31 am »

The driver that I'm working with on this project is the Tang Band W8-1772.

I chose this driver because in a medium-Q sealed box, taking bass boost from the wraparound into account, it should work well crossed over to a Swarm in the 80 Hz ballpark. [Edit: the production version will use a low-tuned vented box and to down to about 55 Hz.]

The W8-1808 has greater linear x-max, but its factory T/S parameters give it more bass extension at the expense of efficiency, and of course call for greater cone excursion to deliver that increased bass extension. For this particular application, the W8-1772 makes more sense in my opinion.

My on-axis measurements do not agree exactly with the published factory curve, but it's reasonably close. On the T/S parameters I trust the factory over my own measurements because I'm not confident that my measurement technique is accurate with such an ultralight, high-compliance cone. Close-miked response in a sealed box is in approximate agreement with the modelled response using the factory parameters.

I've built several prototype enclosures; this is my first real attempt to build such a small offset bipole, and so to certain extent I'm learning as I go. In my opinion the W8-1772 benefits from some electrical filtering, so that's also part of my design.

ttan98 · « **Reply #15 on:** 1 Sep 2009, 10:02 pm »

The cat is out of the bag.

I think you know Bob Brines is conducting FR curve of the same driver. You are right, at some freq range the o/p need some adjustments. At $184 a piece it is by no means cheap, it has to be better than say Alpair10 or Jordan92, it sound quality comparable or better still superior?

Keep us inform. Cheers.

classical music lover · « **Reply #16 on:** 6 Sep 2009, 08:00 pm »

Duke,

My guess was going to be SEAS Exotic single full range driver. It looks like I would have been wrong. Do you investiage the seas Exotic?

JLM · « **Reply #17 on:** 6 Sep 2009, 09:02 pm »

Duke,

I've been playing around with a Behringer DEQ2496 to replace baffle step/zobel circuits on my Bob Brines Fostex F200A based speakers with (IMO) stunning success. As the driver is rated down to 30 Hz raw I thought it would have potential to do even better. It is not an efficient driver and lacks a "nasty" whizzer, but a relatively high quality one that benefits from the EQ, especially at both ends of the frequency spectrum.

Note that I use the DEQ2496 (modded) between transport and monoblocks, so it is also doing DAC duty. In this way my purist tendencies are maintained.

Duke · « **Reply #18 on:** 24 Oct 2009, 06:51 am »

Well with the Tang Band W8-1772 on back-order until December 15th, looks like I'm in the same boat as nearly everyone else: waiting. Apparently Tang Band has a couple of winners in the 1772 and 1808 (though I haven't tried the latter, it sold out just as quickly).

neobop · « **Reply #19 on:** 24 Oct 2009, 09:43 am »

Hi,
I've just started checking out the possibilities for single driver speakers, so I find this thread interesting. I was wondering about Lowther and Audio Nirvana drivers. Any experience with these?
I'm currently using an old 7" Eton woofer pair loaded in an open 8" PVC pipe, that functions as a dipole. I use a Scan Speak 3/4" dome mounted on top of the pipe. Both drivers have very flat response. I looked at the frequency response graphs of the Audio Nirvana and it's not exactly what I'm used to. I was thinking that a zobel might tame the top, but it would kind of defeat the purpose of a speaker sans crossover. Any thoughts on these drivers? should I look elsewhere?
Thanks,
Frank